This application is related to a commonly assigned application by the same inventors entitled Asymmetrical Miniature Bends in Optical Fiber and Method of Forming Same, filed concurrently herewith, the disclosure of which is incorporated by reference herein.
N/A
Fiber optic splitters or couplers are commonly packaged by mounting fused fibers in or on a supporting substrate. Referring to FIG. 1, the fibers have their protective polymer coating removed in a central region of about 2 cm in length. The fibers are fused together in this region to cause a coupling of optical energy (light) between the two fibers. The resulting assembly is quite delicate, because the unprotected optical fibers are exposed in the fusion region, which may have a diameter as small as 20 microns.
To protect the fused fiber assembly, the fibers may be mounted in a protective substrate or package. In one typical example, the fused fibers are placed in a slot in the substrate. The slot forms a protective wrap partially encompassing the fused fibers, which are glued or epoxied within the slot near each end. In the center of the substrate the fibers are freely suspended to avoid optical contact with the substrate or the glue, which would degrade the optical performance of the device. The substrated coupler assembly may then be encased in a polymer tube to provide protection from airborne contaminants during further packaging. This assembly may then be placed inside a tube, such as of stainless steel, to provide final mechanical protection. In this type of splitter, fibers emerge from both ends of the package.
To form a single-sided splitter or coupler, in which fibers enter and exit from one side of the package, it is necessary to turn the fibers back upon themselves to reverse their direction. To avoid light loss and maintain a useful longevity in an unprocessed bent fiber, the turn typically requires a bend radius of 2 cm or more. This radius may be substantially reduced to as little as 50xcexc using miniature bends. To form a miniature bend, the diameter along a length of bare fiber is reduced to as little as 1xcexc or less, by for example drawing, etching, or a combination thereof. In the reduced diameter region, the fiber conducts light by internal reflection at least partially due to the difference in index of refraction at the interface between the fiber and the surrounding environment, generally air. Thus, in this region, the fiber may be bent with no substantial light loss from the bend. See U.S. Pat. Nos. 5,138,676 and 5,452,383, the disclosures of which are incorporated by reference herein.
FIG. 2 illustrates a device in which a miniature bend is packaged within a protective shield or capsule that is closed at one end. In this device, the shield also functions as a strength member to which the miniature bend is mounted to isolate it from external stresses. Adhesive must be inserted inside the shield to bond the fiber leads to the shield, a tedious and exacting process.
Another disadvantage of single-sided splitters or couplers or other components that may utilize known prior art miniature bends is that separate elements must be used, one for the component and one for the bend. Space must be provided between the component and the bend to allow for fabrication of each, resulting in a device that is significantly longer than the component and the bend individually. The device is also less environmentally stable, because the individual component and the bend can move relative to each other, causing additional stress on the fibers.
The present invention provides a fiber optic assembly in which a fiber optic component and a miniature bend are mounted in an integral assembly. The resulting assembly is shorter, more environmentally stable and more robust, because there is no relative motion between components. The resulting device also has fewer parts and processing steps to manufacture.
More particularly, the present invention provides a fiber optic assembly comprising a fiber optic component and a miniature bend fixedly mounted to a substrate. The component comprises at least one optical fiber having an entering fiber portion and a return fiber portion. A buffer covers at least a portion of the return fiber portion and of the entering fiber portion. The bend is formed in an intermediate portion that comprises a bared optical fiber portion between the entering fiber portion and the return fiber portion to provide a reversal of direction between the entering fiber portion and the return fiber portion. The bend is fixedly mounted to the substrate.
In a particular embodiment, the fiber optic component comprises a fiber optic splitter or coupler. Two fibers enter the component from one side. On the other side, two miniature bends are formed to fold the two fibers back upon themselves. The two fibers then exit the component from the same side that they entered. More specifically, entering fiber portions are fixedly mounted within a channel in a substrate by glue or epoxy bonds near the channel ends. Bared fiber portions of the entering fiber portions are fused together in a central fusion region suspended within the channel between the glue bonds to form the splitter or coupler. A further region of bare fibers is provided outside the opposite side of the substrate. The miniature bend is formed in this further region to cause the fibers to reverse direction and extend back upon themselves. Buffered return fiber portions are laid in the channel of the substrate over the entering fiber portions and the fusion region and are fixed above the entering fiber portions by a bond of epoxy or glue over the glue bonds holding the entering fiber portions. The return fiber portions emerge from the substrate directly above the entering fiber portions. In this manner, the miniature bend is rigidly attached to the same structural supporting member, the substrate, as the fusion region, resulting in a construction having stability, rigidity and compact size.